spin/sdk/rust

The Spin Rust SDK

The Spin Rust SDK makes it easy to build Spin components in Rust.

Writing Spin HTTP components in Rust

This library simplifies writing Spin HTTP components. Below is an example of such a component:

// lib.rs
use anyhow::Result;
use spin_sdk::{
    http::{Request, Response},
    http_component,
};

/// A simple Spin HTTP component.
#[http_component]
fn hello_world(req: Request) -> Result<Response> {
    println!("{:?}", req.headers());
    Ok(http::Response::builder()
        .status(200)
        .header("foo", "bar")
        .body(Some("Hello, Fermyon!".into()))?)
}

The important things to note in the function above:

• the spin_sdk::http_component macro — this marks the function as the entrypoint for the Spin component
• the function signature — fn hello_world(req: Request) -> Result<Response> — the Spin HTTP component uses the HTTP objects from the popular Rust crate http, and the request and response bodies are optionally using bytes::Bytes

Making outbound HTTP requests

This library includes the ability to send outbound HTTP requests using the DeisLabs WASI experimental HTTP library.

Let's see an example where the component makes an outbound HTTP request to a server, modifies the result, then returns it:

#[http_component]
fn hello_world(_req: Request) -> Result<Response> {
    let mut res = spin_sdk::http::send(
        http::Request::builder()
            .method("GET")
            .uri("https://fermyon.com")
            .body(None)?,
    )?;

    res.headers_mut()
        .insert(http::header::SERVER, "spin/0.1.0".try_into()?);

    Ok(res)
}

In order for the component above to be allowed to make the outbound HTTP request, the destination host must be declared in the Spin application configuration:

[[component]]
id = "hello"
source = "target/wasm32-wasi/release/spinhelloworld.wasm"
allowedHttpHosts = [ "https://fermyon.com" ]
[component.trigger]
route = "/hello"

Making a request to this component, we can see the appended header, and that the response contains the expected body:

$ curl -I localhost:3000/hello
HTTP/1.1 200 OK
content-length: 29350
content-type: text/html; charset=utf-8
server: spin/0.1.0